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Fluid Catalytic Cracking (FCC) is one of the most important conversion processes used in refineries all over the world. It is used for the conversion of heavy oil feed with high boiling temperature to produce gasoline, diesel, propylene and other valuable products. Coke deposits on the catalyst during the catalytic conversion and deactivates it, therefore catalyst is continuously regenerated in the FCC process. The regeneration step is essential as it directly impacts the products yields. The coke combustion also generates NOx and SOx emissions which levels are highly influenced by the bed hydrodynamics, the operation parameters and the reactor configuration, and are important to quantify. For all these reasons, the understanding of the regenerator hydrodynamic and kinetic is essential. This paper presents a study on the coupling of Barracuda™ CFD code with a coke combustion kinetic model developed at IFP Energies nouvelles to simulate an industrial FCC regenerator. Regenerator operating and performance data, including catalyst samples for coke analysis, are acquired on a selected industrial unit to evaluate the model. The results provide useful insight on the regenerator performance characteristics in terms of air distribution, coke burning rate and temperature profile in the regenerator. The steady state flue gas composition and regenerator dense and dilute phase temperatures are well predicted by the CFD simulation. The CFD prediction of the bed density is underestimated compared to the industrial data. The duration required to completely regenerate the catalyst is also estimated from the results. The CFD coupled coke combustion kinetic model presented in this paper enables us to evaluate the influence of the fluidized bed hydrodynamic on the catalyst regeneration in an industrial FCC regenerator. The developed model serves as a useful tool for the evaluation of future technology development in the FCC regenerator. [ABSTRACT FROM AUTHOR]

• A novel valve mechanism with solvent freezing using recirculating jackets was developed. • A wide range of recirculating flow-rates were tested using computational fluid dynamics. • Several prototypes were 3D-printed in a titanium alloy and tested for pressure resistance. • The switching times and dead volumes were measured for a range of heating-jacket temperatures. In this paper, we demonstrate a proof-of-principle of a freeze-thaw valve (FTV) created in a 3D-printed fluidic device. Portions of channels are enveloped by cooling and heating jackets, and a heat transfer liquid is recirculated through the two jackets. A frozen plug is created in selected portions of the target-channel and the heating jacket ensures that a selected temperature is maintained in the rest of the channel. An FTV can be 3D-printed in a wide variety of materials as single piece devices with no moving parts without high resolution requirements of the printing process. Such valves can therefore be incorporated in devices for liquid chromatography or multi-step synthesis process. Computational fluid dynamic simulations of a prototype T-junction piece show the two zones to be well defined at coolant and heating jacket flow-rates greater than 1 mL/min, with power consumptions of 1–3 W. The prototype was printed in Titanium 6Al-4V using selective laser melting and the frozen plug was shown to withstand 20 MPa of pressure. Switching times between states 1 (with a frozen section) and 2 (with both sections thawed) were 0.2–3 min in computational and experimental tests. The scalability of the freeze-thaw system was demonstrated using a multi-gate valve containing 33 junctions without a proportionate increase in operational complexity or switching times. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, there has been a rapid growth of research and development activities on high temperature molten salts for nuclear and non-nuclear applications. The study of their heat transfer characteristics is a key issue in the current development of the molten salt reactor (MSR) that is one of the innovative nuclear reactors proposed by the Generation IV International Forum. The MSR is a sort of circulating fuel reactor (CFR), which adopts a molten halide salt mixture containing the fissile material and playing the distinctive role of both fuel and coolant. In a thermal-neutron-spectrum MSR, the reactor core is composed by a graphite matrix (neutron moderator), through which the liquid nuclear fuel flows and leads to a strong and intrinsic coupling between thermo-hydrodynamics and neutronics. This peculiar feature requires a suitable and qualified multi-physics simulation environment for a proper description of the system (fuel/coolant+graphite) behaviour. With reference to such complex and non-linear system, the present work is intended to give two different but linked contributions, in the perspective of a multi-physics modelling able to accurately describe the synergy of the involved different physical phenomena (e.g., by means of software). [(I)] On one hand, this work is aimed at establishing a useful validation framework for the assessment of computational fluid-dynamics (CFD) analyses of liquids with internal heat generation. For this purpose, an analytic approach for both fluid velocity and temperature fields in a circular pipe surrounded by a solid region has been developed. It is an extension of the approach elaborated for pipe flow in (Di Marcello, V., Cammi, A., Luzzi, L., 2010. A generalized approach to heat transfer in pipe flow with internal heat generation. Chemical Engineering Science 65, 1301−1310), in order to take into account the heat conduction in the solid domain (represented by the graphite matrix in the specific case of interest). [(II)] On the other hand, the paper presents a preliminary investigation of the thermal-hydraulic behaviour occurring in a typical graphite-moderated MSR core channel. The developed analytic approach has been conveniently applied to this case study: (i) by testing the capabilities of to evaluate the heat transfer characteristics and the hydrodynamic behaviour of such system; and (ii) by investigating the applicability of correlations for the Nusselt number to fluids with internal heat generation. For a deeper insight into the numerical solutions provided by COMSOL, a code-to-code comparison has been also carried out, adopting a dedicated CFD finite volume software (i.e., FLUENT®). As a result, a satisfactory agreement has been found between the analytic solution and the numerical computations provided by COMSOL and FLUENT for a wide range of Reynolds numbers. As concerns the Nusselt number evaluation, the correlations usually adopted for molten salts have been proved as unsuitable for the analysed system, whereas the correlation advanced in the above mentioned paper (that explicitly takes account of the internal heat source) appears more appropriate. The results of the present work are thought to be useful because they provide: (i) a “generalized” analytic approach to the heat transfer that is applicable in a more general context; (ii) an insight into the heat transfer characteristics of the considered graphite-moderated MSR core channel; and (iii) a preliminary assessment of computations that is essential in view of the adoption of multi-physics tools (like COMSOL) for more complex and representative simulations of the dynamic behaviour of the molten salt reactor, and more in general of other kinds of CFRs. [Copyright &y& Elsevier]

Abstract: Randomly packed bed reactors are widely used in chemical process industries, because of their low cost and ease of use compared to other packing methods. However, the pressure drops in such packed beds are usually much higher than those in other packed beds, and the overall heat transfer performances may be greatly lowered. In order to reduce the pressure drops and improve the overall heat transfer performances of packed beds, structured packed beds are considered to be promising choices. In this paper, the flow and heat transfer inside small pores of some novel structured packed beds are numerically studied, where the packed beds with ellipsoidal or non-uniform spherical particles are investigated for the first time and some new transport phenomena are obtained. Three-dimensional Navier–Stokes equations and RNG k–ε turbulence model with scalable wall function are adopted for present computations. The effects of packing form and particle shape are studied in detail and the flow and heat transfer performances in uniform and non-uniform packed beds are also compared with each other. Firstly, it is found that, with proper selection of packing form and particle shape, the pressure drops in structured packed beds can be greatly reduced and the overall heat transfer performances will be improved. The traditional correlations of flow and heat transfer extracted from randomly packings are found to overpredict the pressure drops and Nusselt number for all these structured packings, and new correlations of flow and heat transfer are obtained. Secondly, it is also revealed that, both the effects of packing form and particle shape are significant on the flow and heat transfer in structured packed beds. With the same particle shape (sphere), the overall heat transfer efficiency of simple cubic (SC) packing is the highest. With the same packing form, such as face center cubic (FCC) packing, the overall heat transfer performance of long ellipsoidal particle model is the best. Furthermore, with the same particle shape and packing form, such as body center cubic (BCC) packing with spheres, the overall heat transfer performance of uniform packing model is higher than that of non-uniform packing model. The models and results presented in this paper would be useful for the optimum design of packed bed reactors. [Copyright &y& Elsevier]

Two-phase flows are regularly involved in the heat and mass transfer in industrial processes. To ensure the safety and efficiency of such processes, an accurate prediction of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) is required. Nowadays, Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore, the Euler–Euler framework is often employed for large-scale simulations, which involves macro-scale modelling of turbulence, mass and momentum transfer. The research activities at Helmholtz–Zentrum Dresden–Rossendorf (HZDR) focus on general closure models for multiphase flows that are closer to physics and include less empiricism. As part of this effort, an Algebraic Interfacial Area Density model (AIAD) is developed for the morphology detection in the two-fluid Euler–Euler approach. Drag models for free surface flows are often based on experimental correlations, their applicability thus being limited to certain flow regimes. In this paper, a modified free-surface drag model based on local shear stress is investigated that avoids this limitation. For this purpose, the algebraic morphology detection mechanism of the AIAD model is revised. In DNS of free surface flow a dampening of the gas side turbulent fluctuations in the near surface region was found by previous investigators. This effect has also been accounted for in Euler–Euler simulations by means of dampening functions. In this work, the significance of turbulence dampening, in case of free surface flows, is examined quantitatively for the k – ω turbulence model. Model validation is performed with the commercial CFD code ANSYS CFX by means of experimental data of countercurrent, supercritical stratified air–water flow. The revised morphology detection mechanism is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag model based on experimental pressure difference, liquid levels and interfacial shear stress. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in the k – ω model to qualitatively reproduce the mean flow and turbulence quantities from the experiment. More CFD grade experimental data is required for further model validation. [ABSTRACT FROM AUTHOR]

This paper presents a constitutive equation for the thermal heat transfer associated by mass transfer, applicable to both Eulerian–Eulerian and Eulerian–Lagrangian multiphase computational fluid dynamic models. The proposed equation was incorporated into the open-source multiphase CFD code MFIX ( https://mfix.netl.doe.gov ) to demonstrate that the numerical predictions match experimental data for the limiting cases of evaporation and condensation. The application of the proposed equation to two cases of a reacting carbon particle yields physically consistent expressions for the heats of reaction. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyses reaction and thermal front development in porous reservoirs with reacting flows, such as those encountered in oil shale upgrading. A set of dimensionless groups and a 1D code are developed in order to investigate the important physical and chemical variables of such reservoirs when heated by in situ methods. Theory necessary for this study is presented, namely shale decomposition chemical mechanisms, governing equations for multiphase flow in porous media and necessary closure models. Plotting the ratio of the thermal front speed to the fluid speed allows one to infer that the reaction front ends where this ratio is at a minimum. The reaction front follows the thermal front closely, thus allowing assumptions to be made about the extent of decomposition solely by looking at thermal front progression. Furthermore, this sensitivity analysis showed that a certain minimum permeability is required in order to ensure the formation of a traveling thermal front. Compared to varying deposit porosities and kerogen activations energies, varying temperature, pressure and permeability are more important. [Copyright &y& Elsevier]

Abstract: This paper presents a CFD modeling of hydrodynamics, heat transfer and cracking reaction in a heavy oil riser together with a bottom airlift loop mixer. By extending a validated gas–solid flow model to incorporate feedstock vaporization and 12-lump kinetic model, a three-phase flow and reaction model is established. CFD analysis is performed, and the effects of operating parameters are thus evaluated. The results indicate that the bottom airlift loop mixer causes the hot and the cool catalyst well mix and obtains a uniform catalyst temperature at riser inlet. There exists optimal product distribution, with a maximum light liquid yield at about 30.0m of up the riser. Product yields are more sensitive to injection angle than to feedstock droplet size and reaction temperature. A catalyst-to-oil ratio in the range of 7–8 and a shorter reaction time of 3.02s are preferable for a higher light liquid yield. [Copyright &y& Elsevier]

Abstract: With the study object of an 100kt/a SL-II ethylene cracking furnace, this paper used Computational Fluid Dynamics (CFD) method to carry out coupled simulation studies on the flow, combustion, radiative heat transfer and thermal cracking reaction processes in the cracking furnace. The standard k–ε two-equation model was applied to turbulence simulation. The finite-rate/eddy-dissipation model was used for modeling of non-premixed combustion of the bottom burners and premixed combustion of the sidewall burners. The Discrete Ordinates (DO) model was applied to the simulation of radiative heat transfer of furnace. The simulation results show the detailed information about velocity, temperature and concentration fields in the furnace and heat flux distribution on the reactor tubes skin. This work will provide a theoretical basis for the optimization of the geometrical structure and operational parameters of the cracking furnace. [Copyright &y& Elsevier]

Abstract: Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to flow maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to flow maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a flow maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance. [Copyright &y& Elsevier]

Abstract: This paper proposes a transient three-phase numerical model for the simulation of multiphase flow, heat and mass transfer and combustion in a bubbling fluidized bed of inert sand. The gas phase is treated as a continuum and solved using the computational fluid dynamics (CFD) approach; the solid particles are treated as two discrete phases with different reactivity characteristics and solved on the individual particle scale using an extended discrete element model (DEM). A new char combustion submodel considering sand inhibitory effects is also developed to describe char particle combustion behavior in the fluidized bed. Two conditions, i.e. a single larger graphite particle and a batch of smaller graphite particles, are used to test the prediction capability of the model. The model is validated by comparing the predicted results with the previous measured results and conclusions in the literature in terms of bed hydrodynamics, individual particle temperature, char residence time and concentrations of the products. The effects of bed temperature, oxygen concentration and superficial velocity on char combustion behavior are also examined through model simulation. The results indicate that the proposed model provides a proximal approach to elucidate multiphase flow and combustion mechanisms in fluidized bed combustors. [ABSTRACT FROM AUTHOR]

Abstract: Radial heat transfer in laminar pipe flow is limited to slow thermal conduction which results in a wide temperature distribution over the pipe cross-section. This is undesirable in many industrial processes as it leads to an uneven distribution of fluid heat treatment. Often the fluids involved are relatively viscous and processing them under turbulent conditions is impractical and/or uneconomical. On the other hand, the use of static in-line mixers to promote radial mixing may be prohibited in hygienic processes because they are difficult to keep clean. In this paper, we use a validated Computational Fluid Dynamics (CFD) model to show that the imposition of a transverse vibration motion on a steady laminar flow generates sufficient chaotic fluid motion which leads to considerable radial mixing. This results in a large enhancement in wall heat transfer as well as a near-uniform radial temperature field accompanied by a substantial heating of the inner region of the flow. Vibration also causes the temperature profile to develop very rapidly in the axial direction reducing the thermal entrance length by a large factor, so that much shorter pipes could in principle be used to achieve a desired temperature at the outlet. The effects are quantitatively demonstrated for Newtonian and non-Newtonian pseudoplastic fluids of different viscosities, for a wide range of vibration amplitudes and frequencies. For processes where vibrational motion can be implemented the benefits can be very significant. [Copyright &y& Elsevier]

Abstract: The hydrodynamics and heat transfer characteristics of a heat exchanger with single-helical baffles are studied experimentally as well as numerically. A heat exchanger with two-layer helical baffles is designed by using computational fluid dynamics (CFD) method. The comparisons of the performance of three heat exchangers with single-segment baffles, single-helical baffles and two-layer helical baffles, respectively, are presented in the paper. The experiment is carried out in counter-current flow pattern with hot oil in shell side and cold water in tube side. Overall heat transfer coefficients are calculated and heat transfer coefficients of shell side are determined by Wilson plots technique. It shows that the heat exchangers with helical baffles have higher heat transfer coefficient to the same pressure drop than that of the heat exchanger with segmental baffles based on the present numerical results, and the configuration of the two-layer helical baffles has better integrated performance than that of the single-helical baffles. [Copyright &y& Elsevier]

• This paper develops a solver based on the open source toolbox OpenFOAM. • The coupled heat transfer between gas, catalyst, reactor, and coolant is solved. • Two-temperature model calculates the temperature of gas and catalyst is adopted. • The solver coupled with a reaction model reproduces observed temperature profile. Methanation is one of the promising candidates in developing CO 2 utilization technology. Because of its exothermic behavior, the methanation reactor must be carefully designed to avoid the hotspots formation and the deterioration of catalysts. This study presents a numerical study simulates heat transfer between the reacting gas in a porous catalyst layer, reactor tube, and coolant in a shell-and-tube reactor. The aim is to develop a tool can predict the hotspots appearing in the reactor used in CO 2 methanation. The open-source toolbox OpenFOAM is adopted and modified. The catalyst bed is assumed to be a continuous porous medium. The results revealed that the solver captures the trends of temperature profiles along both axial and radial directions. The maximum catalyst temperature predicted by this solver is in good agreement with the experimental result, indicating that the solver is a promising tool for future applications in reactor optimization and heat management. [ABSTRACT FROM AUTHOR]